Prior Art
Pump systems for removing subsurface fluids, such as oil or water, normally include a pump assembly which is reciprocated in a working barrel through which the oil or water is drawn upwardly to the top of the wellhead. The pump assembly is normally driven by a drive unit which reciprocates the pump assembly through a pump or sucker rod. The pump rod is attached between the drive unit located at or near the wellhead and to the pump assembly located below the wellhead.
Because of the possibility that the pump assembly may become stalled in the working barrel, it is necessary to provide a system which will drive the pump rod under normal load conditions but which will cease operation is the event the downhole pump assembly is stalled. Such an arrangement prevents damage to the downhole structure as well as the drive unit used to drive the pump assembly.
While fluid pressure has been used to drive a motor which in turn drives the pump rod, past systems have not adequately provided for the situation where the pump piston is stalled in the downhole line. Further, past drive systems have failed to provide adequate control on the rate of operation of the downhole pump or the pump stroke. The pump drive system must also provide for expansion of gases and fluids within the system as a result of variation in ambient temperatures. Systems now in use fail to compensate for such expansions in a way compatible with the operation of the drive unit. Further, presently used units are of a size generally requiring the construction of considerable foundations on which they are supported.